1. Field of the Art
This invention relates to a process for producing an aromatic sulfide polymer according to the dehalogenation/sulfidation reaction of a dihalo-aromatic compound with a metal sulfide. More specifically, the present invention relates to a process for producing an aromatic sulfide polymer having a markedly high molecular weight with extremely good reproducibility which has a primary feature in practicing this reaction according to a specific method.
In recent years, it has been required of thermoplastic resins for use as members or parts in electronic appliances or automobile appliances to have still higher heat resistance. Aromatic sulfide polymers are endowed with properties of a resin which can meet such a requirement. However, due to the nature of this resin conventionally produced such that a polymer endowed with high crystallinity and with sufficiently high molecular weight can hardly be obtained, it is very difficult to fabricate the resin into films, sheets or fibers and there is also a great problem that the formed product is very brittle. The present invention is to overcome these problems, and provides a process for producing a linear aromatic sulfide polymer having a markedly high molecular weight.
2 Prior Art
The following processes have been known for production of aromatic sulfide polymers.
(1) A process in which elementary sulfur, dichlorobenzene and a base (e.g., Na.sub.2 CO.sub.3) are caused to react in the molten state in the absence of a solvent (e.g., U.S. Pat. Nos. 2,513,183 and 2,538,941).
(2) A process in which an alkali metal sulfide, particularly hydrous Na.sub.2 S, is heated in a polar solvent to remove the water of hydration in the hydrous Na.sub.2 S, dichlorobenzene is added thereto and polymerization under heat is carried out (e.g., U.S. Pat. No. 3,354,129).
(3) A modification of the above process (2), in which the step of dehydration is conducted in the presence of a carboxylic acid salt, dichlorobenzene is added thereto and polymerization under heat is carried out (e.g., U.S. Pat. Nos. 3,919,177 and 4,089,847).
However, to the best knowledge of the present inventors, these processes are not very satisfactory. For example, according to the above process (1), the resultant polymer has a molecular weight which is too low and therefore it may be difficult to obtain a practical linear aromatic sulfide polymer. According to the process (2), a polymer having a molecular weight slightly higher than that of the polymer of the process (1) can be obtained, but yet it may be difficult to obtain a polymer having a high molecular weight sufficient enough for a practical linear aromatic sulfide polymer. The process (3) has been proposed for the purpose of overcoming the problem inherent in the process (2) that molecular weight of the resultant polymer is not very high and the improvement has in fact been made to a considerable extent. However, even according to this process, so far as the present inventors know, it may be considerably difficult to obtain a polymer having a high molecular weight sufficient enough for producing tough films, sheets and fibers with good reproducibility. Reproducibility is of a particular importance in commercial production.
The primary reasons why it is difficult to obtain a polymer of high molecular weight with good reproducibility may be attributed to the fact that the water is removed from hydrous Na.sub.2 S (including the reaction product formed in situ between hydrous NaHS and NaOH), which is one of the starting materials, through evaporation by heating the hydrous Na.sub.2 S in a polymerization solvent, whereby (a) sufficient dehydration is hardly possible, and it is difficult to control the residual water content, (b) during the dehydration the sulfur content in the metal sulfide is entrained with the water as, e.g. H.sub.2 S to be a loss, with the result that the amount of the sulfur content present in the reaction system is fluctuated, and (c) under the state where water remains in a considerable amount, the metal sulfide will corrode the reaction vessel used, and the heavy metal ions dissolved out due to the corrosion inhibit formation of a polymer of a high molecular weight.
Still another problem of the process (3) may reside in that polymerization conducted in the presence of a large amount of a water-soluble organic salt will result in formation of aqueous waste containing a large amount of the salt dissolved therein, whereby a problem of environmental pollution may occur and a considerable amount of cost is required for removal of such a problem.